Gun Light, CR123 or CR2, Need LiFePO4 EXACTLY 3.25 V - 3.30 V

Batteries and Chargers Rechargeable Batteries
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Hi All. My name is Ron. Just recently discovered this forum and joined. Please be gentle if I make any errors. This gets a bit long but please bear with me. I try to share any useful info I’ve found that might be helpful to others.

I did read the sticky in this forum category of CR123A rechargeable replacements.

I have an issue I’ve been researching for a week via Google, DuckDuck Go, Brave Search. I’ve been reading many dozens of articles and watching dozens of videos. I’ve read threads on forums such as this and others. I have not found a solution.

I have the following weapon lights which use CR123A primary batteries:

https://www.opticsplanet.com/v/69424-streamlight-tlr-7a-flex-tactical.html

https://www.opticsplanet.com/v/69414-streamlight-tlr-8a-flex-tactical.html

I also have the following laser which uses a CR2 battery:

StrongTools Red or Green BoreSighter
https://www.amazon.com/gp/product/B07DZ5BYFG/

I wish to be able to use these devices for training purposes with rechargeable LiFePO4 batteries. For non training use, I may revert back to the primary batteries. I know primary’s can be had for $ 1-2 each, but bear with me. Streamlight docs and tech support don’t recommend rechargeable’s and are no help.

I know that LiFePO4’s come off the charger at around 3.7 V. I also know that they stabilize to around 3.34 V. From research, I’ve determined that CR123A primary batteries come out of the box with a voltage of 3.0 V - 3.3 V (according to a Duracell spec sheet). I’ve read anecdotal evidence of the voltage sometimes being higher. I measured some of my own primary batteries and got 3.25 V for a CR123A and 3.29 V for a CR2.

Since these primary batteries may routinely be 3.3 V out of the box, I have to assume that the lights and lasers will handle 3.3 V without a problem.

So, my intention is to either discharge a fully charged LiFePO4 battery to EXACTLY 3.25 V - 3.30 V, with 10 mV accuracy; or to charge a discharged LiFePO4 battery to this voltage. The battery must not creep above 3.30 V, not even to 3.31 V. Under those conditions, I should be completely safe putting the rechargeable battery in the light or laser. There should still be some usable energy in the battery before it gets down to around 2.5 V - 2.8 V, etc.

I have this electronic load:

East Tester ET5410 Single-Channel Programmable Electronic Load 400W

I jerry-rigged a way to attach clip leads to the battery using a paper clip and rubber bands.

I have the following battery holders on order to make this easier.

Battery Enclosures SMT BATTERY HOLDER CR123A
https://www.mouser.com/ProductDetail/534-1050

Battery Enclosures SMT BATTERY HOLDER CR2
https://www.mouser.com/ProductDetail/534-1010

I am using this RCR2 battery:

CR2 Rechargeable Battery and Charger 15270 3.0V Battery
https://www.amazon.com/gp/product/B09FGPTT37/

and this RCR123A battery:

SureFire SFLP123 3V Lithium 1550mAh 2 Pack Battery (note the capacity is wrong there)
https://www.amazon.com/gp/product/B08MZCQ6T3/

(Interesting that the descriptions say 3 V, when in fact, these might damage equipment that runs on 3 V primary’s.)

I’ve currently been testing the CR2, which has a 300 mAH capacity.

So, my first thought was to set the load bank to drain at 100 mA down to 3.25 V. That failed. I’m assuming there was too much voltage drop initially and the load bank turned off. I am able to set the low voltage cutoff to 3.00 V and the load bank runs, but I have to manually monitor the actual voltage and stop the process. Also, once I do stop it, the voltage starts creeping back up on the battery.

That’s as far as I’ve practically gotten. I did confirm that I would have some usable energy left in the battery after treating it thus, although not obviously all of the energy. I have considered a crowbar circuit across the battery with a zener diode and a current limiting resistor and maybe a LED indicator light, but zener diodes are not generally very precise. I have also considered a precision charging circuit to go up to 3.30 V. But, I haven’t gotten any further.

So, if anyone knows how I could either discharge the LiFePO4 to exactly 3.25 V - 3.30 V (even at rest) or how I could charge the battery to exactly 3.30 V with 10 mV accuracy, I’d very much appreciate learning it. I want to be able to just charge then drain the battery or just partially charge the battery then pop it into the light or laser without blowing anything up.

Thanks in advance for any and all help. I have a feeling that, if we find a solution, there would be people other than myself interested in it. If you build it and get rich, send me a share. :smiley:

Ron

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I wouldn’t actually be too worried about the light running on even a fully charged LiFePO4 cell.

There are actually plenty of Streamlight owners using 3.2V lithium ion LifePO4 16340s and their lights have been running in tip top shape, unlike those running normal 3.6V nominal lithium-ion 16340s.

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The LiFePO4 chemistry voltage does not change much during discharge, so discharging it it get to a specific voltage might not work well.

The LiFePO4 cell might work fine in your light without any changes. Flashlights are designed to work with a range of voltages, and LiFePO4 usually stays at ~3.2V under load. See here for an example.

You could contact streamlight and ask if LiFePO4 can be used in the lights, or what the acceptable input voltage range is.

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I use LFP in my streamlights with no problems. I have a feeling Streamlight warns against rechargeables because 3.7v lithium chemistries are much more common and cheaper than LFP, and customers are likely to confuse 3.2 and 3.7 cells.

There’s a much bigger difference between an LFP at 3.3 and a primary at 3.0 when compared to a 3.7 that can rest at 4.1 fully charged.

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BlueSwordM, achilles’ spiel You make some interesting points. I wonder if anyone is using the specific streamlights that I mentioned. I’m really reluctant to try experiments on lights which cost $ 125 - $ 200. These particular lights don’t have what I’d call a physical on off switch. They do have a button, but I’m thinking the logic board actually switches the light / laser on. The idea of hitting that with up to about 3.7 V initially makes me nervous.

@EasyB That’s a very interesting graph you posted. I wonder how long it takes for the voltage to drop down from the no load peak and how many uS or mS it takes. I called Streamlight and the only thing they’ll say is that they don’t support or endorse rechargeable batteries for these lights.

Ron

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EasyB nailed it with respect to discharge voltage: LFP discharge is very flat. At low current draw, LFP is near half discharged at 3.0v even. Here’s another, more general article on this from BU: BU-903: How to Measure State-of-charge - Battery University

The easiest and safest option is to eat the cost and continue using primaries.

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Looks like a cool article. I’ll look that over. Thanks. :sunglasses:

Ron

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Hi all. I may have found a solution to my problem, which I describe here. Unfortunately for the readers, my solution involves the use of some specialized equipment that I have, specifically the electronic load bank I mentioned in the first post. But, I’m passing along the information in case it’s useful to you all. There still may be better and cheaper ways to do this. I suspect it could be done with $ 5 worth of components if they were the right components.

I was playing around with the load bank menus. I found a setting for CV (constant voltage) which seems to fit my needs. Remember this is a load bank, not a charger. In CV mode, it puts a variable load on the object under test (battery) and increases the load until the voltage drops to the specified value. Or, if necessary, it decreases the load (or doesn’t ever start) until the voltage reaches the specified value.

The net result is, assuming the battery voltage starts out above the set point, that the load bank continually increases current draw until the voltage drops to the specified value. As the battery discharges, the current drain will continually drop to maintain the voltage at the set point. There is also an option to have the unit turn off after a certain amount of time, as, like discharging a capacitor, current may never actually reach zero.

This theoretically should do what I want. The load bank tries to reach the set voltage as soon as it’s turned on. It doesn’t gradually go to that voltage. Setting the voltage set point could be very dangerous if it’s too low. For example, suppose I tell the unit to make the voltage .1 V or something ridiculous. It may try to pull up to 40 A (the capacity of the load bank) from the 300 mAH battery. In that case, I imagine bad things happen. So, you want to start with a high voltage set point which translates into very low current.

I have the unit running now. The battery is a 300 mAH RCR2. I set the voltage target at 3.29 V. For some reason it’s pulling it down to 3.27 V. Don’t know why. The initial current started at about 90 mA, which is almost .3 C. It’s been running for 01:15:00 and now the current is down to about 18 mA. I may cut it off at 01:30:00 and see if the settling voltage on the battery stays below 3.30 V. If not, I may zap the battery for another hour. I could also lower the target voltage but that lowers the amount of energy left in the battery to use in my lights or lasers.

Edit: reword for clarity. This technique could also be used to drain a battery for storage but the initial current might be too high if the voltage set point is low. The load bank also has a CC+CV mode that might work for storing batteries. I haven’t played with that. However, I suspect that many of you have chargers / analyzers that can do that as well. I suppose a charger / analyzer with discharge capability could be used as well to get the battery to 3.30 V for my purpose if it allows you to set the target voltage with 10 mV accuracy.

Hope this helps. Ron

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Thanks for joining the party, rfrazier!

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Thank you too. Quite an interesting place. :sunglasses:

Ron

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How much current is drawn from those cells?

There are plain ol’ Li cells that are regulated down to an exact 3.0V. Just don’t use ’em in a light that’s too high-strung, as the regulator board can only handle so much current. But if it’s 2 cells in series, current might be halved vs a single 18650.

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How about these which are regulated to 3V lithium ion cells?

Edit: Lightbringer brought the light right before me :slight_smile:

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Lightbringer, shadow, the regulated Li-Ion’s are an interesting idea. I hadn’t thought of it. I’m strongly attracted to the LiFePO4’s due to safety concerns. The regulated Li-Ion would certainly solve the voltage problem. In terms of current, the data sheets show the capacity of CR123A’s is 1500 mAH down to 2 V. The ad for the TLR-8A and 7A gun lights (which use one CR123A battery) on OpticsPlanet claims the light has 1.5 hr battery life. So, doing a bit of math, I would estimate that the current drain at about 1 A. So that part might work. I don’t have any specs on the bore sight laser which uses the CR2 battery. One of the comments for the battery shadow mentioned says it’s too long. It does look like it’s 36 mm long rather than 34 mm. So, I doubt it would fit. (Hopefully the LiFePO4 will even fit.) Finally, since this is a gun light, it will be subject to lots of jarring and shaking when the gun is fired. So, I would wonder what the effects would be on the circuit board. Technically, I don’t even know how that will affect the LiFePO4. So, the Li-Ion’s might not be the best for this application. It’s a cool idea though and it’s good to know those products are available. Thanks for the tip. :sunglasses:

Ron

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CR123s drop off their fresh peak voltage fairy rapidly under load from what I’ve read. Perhaps the makers take this into account when specking out their drivers.

You could pickup a relatively inexpensive Voltage and Current controlled power supply and charge any battery to your desired voltage.
All the Best,
Jeff

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Hi Jeff. I’m in the process of draining the batteries to 3.27 - 3.29 volts with my electronic load. Assuming the battery voltage doesn’t creep up too much afterward, that will probably work. Then I’ll test with the lights / lasers. It would be interesting to work the other way around like you said. The catch would be that the power supply voltage control and measurement systems would need to be accurate to 10 mV. I have a power supply with analog knob controls, but it’s voltage measurement system is only accurate to 100 mV. The charging procedure would probably be easier than charging then draining with the right equipment. Ron

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Ron,
I have one of these DROK buck supplies.
https://www.amazon.com/DROK-Converter-5-3V-32V-Regulator-Transformer/dp/B078Q1624B/ref=sr_1_5?crid=18FISVWSRRIEK&keywords=drok%2Bbuck%2Bconverter&qid=1651783635&sprefix=drok%2Bbuck%2Caps%2C683&sr=8-5&th=1

from the Ad copy: “This Buck Converter is equipped with LCD Display, Acrylic Case and Heat Sink. LCD Screen can display input/output voltage, output current and output power. Voltage precision is 0.05V, current precision is 0.005A. ”

The adjustment is fairly fine - as in many turns to change the V or C.
Calibrate it with a real volt meter and you could be good to go.

Not sure I’d spring for a more expensive bench type supply for a project like this.
Still - any excuse to buy more toys - is usually enough justification for me.
All the Best,
Jeff

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I’ve been following this thread and tried the same a few years ago. For myself and a few other deputies LiFePO4’s couldn’t keep up even in training. They just drain too fast. Considering 1 battery is cheaper than a few rounds I went with Titanium Innovations. $1.10 for CR123a’s or CR2’s. We did bulk purchase through our county and got them down to 80 cents apiece. With a ten year shelf life they’ll get used.

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Jeff, you said “any excuse to buy more toys”. I like the way you think. That is an interesting device. I have a couple of DROK things around here. One of which I like (a mini square wave generator). The other (a voltage current power meter) was horribly inaccurate. The device you mentioned looks interesting. I assume it will output a constant voltage unless the current hits the limit. .05 V isn’t really enough resolution but, as you said, I could calibrate with a voltmeter if the pot is sensitive enough. I guess, now that you mentioned it, I could calibrate my bench power supply with a voltmeter even though it’s display only has 1 decimal place on the voltage. Whether I could tweak the hand knobs to 10 mV, I don’t know. That unit only has a course and fine knob, no multi-turn pots. I got those battery holders I ordered from Mouser. The spring tension is REALLY tight. I almost broke a fingernail trying to get the battery out. But, it definitely does work. SOOO … have you charged any batteries with this device? If so, how did it work?

Texas shooter, you make some interesting points and it brings up some more questions. Unfortunately 1-2 rounds is more than $ 0.80 nowdays. Interesting perspective. I’m not an officer, just an individual. And, with the price of ammo, I doubt I’ll be doing too much training. So, when you tried LiFePO4’s, did you treat them as I am trying to drain them first, or did you just put them in lights / lasers? Did they blow up the lights / lasers? If you use a primary battery for a while in training, do you throw it out (or set it aside) and put a new one in for duty? If you use one for duty for a while, do you throw it out and replace it, lest it fail at a bad time? I like to soak up all the info I can regardless of how this experiment turns out. When I’m not training, I’ll probably keep regular primary batteries in the devices. I’m about ready to pull the batteries I’ve been draining off the load bank and test them. I’ll pass along whatever I find out.

Ron

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I tried 2-3.6v LiFePO4’s and 1-4.2v Lithium-ion from Keepower 16340 700 mah, with dummy in the TLR-1 HL. Both worked, with the 4.2v with dummy not as bright. Soshine RCR123 3.0V 650mAh used a built in diode to actually lower output to 3.1 volts but needed 4.35 volt charger to fully charge. CR123a’s don’t suffer much loss until about 3 amps. So CR123a’s give you about 1400mah of runtime. Soshine RCR123 3.0V alternates gave 325mah and Keepower 16340 700mah gave 600mah. These number were gotten from https://lygte-info.dk he goes by HKJ on this board and Candlepower. Experimenting was eating into actual training and practice. If you train with gear that you don’t actually use your cheating yourself. I use the same magazines, firearms, lights and bullet weights in training as duty or now home defense. I know what my lights will do. Do you know the difference in output and runtime between the rechargeable and the primary? Does it affect spill enough to change what you can or can’t identify.

After the experimental phase ended it was always Titanium Innovations, they work and are cheaper than Panasonic. Used batteries get marked with a sharpie and used in other devices. It’s always an unused or slightly used battery in the weapon light because they just don’t really ever get any use on duty. They get used during training much more but only for minutes. So maybe 1-2 sets a year and that includes the shotgun and carbine. I’m recently retired but still keep an extra set in the drop bag and the lightweight response harness. Batteries are easy and small enough to store in rifle or shotgun pistol grips, waterproof soda preforms vs how many you actually need or use. That 10 year shelf life keeps peace of mind.

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Hi Texas Shooter. I really appreciate all the valuable information you (and others) are sharing. I’m learning quite a bit. I’m sitting here watching the gun laser draining the RCR123, watching the load bank drain another, and watching the TV news. I figured why not add a 4th thing to do so I’m typing this. Once the laser expires, I’ll post my testing results for the rechargeable LiFePO4’s. I found a number of your comments very interesting, and I definitely appreciate the advice regarding training.

“TLR-1” - cool. At least that’s the same brand as some of my products.

“So CR123a’s give you about 1400mah of runtime.” - I note that is 100 mAH less than the rating.

“Soshine RCR123 3.0V alternates gave 325mah” - OUCH. That’s about 125 mAH less than the rating of my Surefire RCR123’s. But, it’s about 325 mAH less than the rating you quoted for it. Yuck.

“Keepower 16340 700mah gave 600mah.” - Also 100 mAH less than the rating.

So, correlating all that, the rechargeable’s are giving substantially less output than the primaries. That’s unfortunate and frustrating. This correlates with the testing results I’m getting. I don’t know how much training I’ll be doing with the lights, but that may have to be with primary batteries. Even if I consume a couple per month, that’s not a crushing expense. I like the idea of separating the used batteries from the new ones and keeping new ones on standby in the lights.

“easy and small enough to store in rifle or shotgun pistol grips, waterproof soda preforms” - Those are cool ideas.

Ron